Question

Which of the following chemical reactions is an example of a combination reaction?
A.$Ca\left(s\right)+2HCl\left(aq\right)⟶CaC{l}_2\left(aq\right)+H_2\left(g\right)$
B. $2KCl{O}_3\left(s\right)⟶2KCl\left(s\right)+3O_2\left(g\right)$
C.$2H_2{O}_2\left(l\right)⟶2H_2\left(g\right)+O_2\left(g\right)$
D. $2S\left(s\right)+3O_2\left(g\right)⟶2S{O}_3\left(g\right)$

• A.
• B.
• C.
• D.

Answer 1

The correct option is D
Displacement Reaction: Those reactions in which highly reactive elements displace the less reactive element from its compound.
$Ca\left(s\right)+2HCl\left(aq\right)⟶CaC{l}_2\left(aq\right)+H_2\left(g\right)$
In this reaction Ca displaces the hydrogen due to its high reactivity.
Decomposition Reaction: Those reactions in which a single reactant decomposes into two or more products.
$2KCl{O}_3\left(s\right)⟶2KCl\left(s\right)+3O_2\left(g\right)$
$2H_2{O}_2\left(l\right)⟶2H_2\left(g\right)+O_2\left(g\right)$
In these two reactions, a single reactant decomposes into two products, hence it is a decomposition reaction.
Combination Reaction: Those reactions in which two or more reactants combine together to form a single product is called combination reaction.
In this reaction, sulphur reacts with oxygen to form sulphur trioxide.
$2S\left(s\right)+3O_2\left(g\right)⟶2S{O}_3\left(g\right)$
Two reactants sulphur and oxygen react to give single product sulphur trioxide, hence it is a combination reaction